As shown by Williams, U.S. Pat. No. 4,273,712, and Williams U.S. Pat. No. 4,257,953, assigned to the same assignee as the present invention, methods are provided for making aromatic bis(etherimide)s of the formula, ##STR1## where R is a monovalent radical selected from hydrogen, a C.sub.(1-8) alkyl radical and C.sub.(6-13) aryl radical, R.sup.1 is a C.sub.(6-30) aromatic organic radical, and a is an integer equal to 1 or 2, and when a is 1, R.sup.1 is monovalent and when a is 2, R.sup.1 is divalent. Reaction is effected between a substituted phthalimide of the formula, ##STR2## and an alkali metal phenoxide of the formula, EQU (R.sup.1 --OM).sub.a ( 3)
in the presence of a nonpolar organic solvent and a phase transfer catalyst, where R, R.sup.1 and a are as previously defined, X.sub.1 is a radical selected from nitro and halo, and M is an alkali metal ion.
The phase transfer catalyst utilized by Williams and Williams et al are tetraorgano ammonium or phosphonium salts, for example, tetraalkylammonium salts, which allow for the production of aromatic etherimides in the absence of a dipolar aprotic solvent. Although valuable results are obtained in accordance with the practice of the Williams, or Williams et al methods, the quaternary ammonium or phosphonium salts are often found to be unstable. The instability of these tetraalkyl salt phase transfer catalyst can result in undesirable phenol alkylation and recycling problems.
The present invention is based on the discovery that aromatic ethers including the etherimides of formula (1) can be obtained without phenol alkylation by utilizing as a phase transfer catalyst in the condensation reaction between a nuclear activated aromatic compound substituted with a leaving group selected from nitro or halo such as the substituted phthalimide of formula (2), and the alkali metal phenoxide of formula (3), an effective amount of a diorganoaminopyridinium salt of the formula, ##STR3## where R.sup.2 and R.sup.3 are monovalent or divalent organo radicals selected from C.sub.(1-13) hydrocarbon radicals and C.sub.(1-13) substituted hydrocarbon radicals and C.sub.(1-8) divalent alkylene radicals which can be part of a cyclic structure forming a C.sub.(4-12) ring, R.sup.4 is selected from C.sub.(4-18) linear or branched alkyl radicals and Y is a counter ion. These diorganoaminopyridinium salts, unlike aminopyridinium salts have also been found to be highly stable as compared to the tetraorganoammonium, or phosphonium salts of Williams, or Williams et al referenced above.
As utilized hereinafter, the term "phase transfer catalyst stability" means the half-life of the catalyst as determined by heating an equal molar amount of phase transfer catalyst and the disodium salt of bisphenol-A in toluene under sealed conditions for a particular period of time which can vary between one-half hour or less to 16 hours or more. Assuming a pseudo-first order for decomposition of the phase transfer catalyst, the amount of catalyst remaining after a certain heating period as determined by NMR analysis can be extrapolated or interpolated to determine the midpoint of the linear plot. This procedure is shown by J. March, "Advanced Organic Chemistry", 2nd Ed., pp. 199-202. This procedure will provide a plot of ln[catalyst] vs. time, and should yield a linear plot.